Single‐Walled Carbon Nanotube Film as an Efficient Conductive Network for Si‐Based Anodes

Abstract

Silicon-based anodes are considered ideal candidate materials for nextgeneration lithium-ion batteries due to their high capacity. However, the low conductivity and large volume variations during cycling inevitably result in inferior cyclic stability. Herein, a dry method without binders is designed to fabricate Si-based electrodes with single-walled carbon nanotubes (SWCNTs) network and to explore the different mechanisms between SWCNT and multiwalled carbon nanotubes (MWCNTs) as a conductive network. As expected, higher initial discharge capacity (1785 mAh g −1 ), higher initial Coulombic efficiency (ICE, 81.52%) and outstanding cyclic stability are obtained from the SiO x @C|SWCNT anodes. Furthermore, its lithium-ion diffusion coefficient (D Li+ ) is 3-4 orders of magnitude higher than that of SiO x @C|MWCNT. The underlying mechanism is clarified by in situ Raman spectroscopy and theoretical analysis. It is found that the SWCNTs can maintain good contact with SiO x @C even under tensile stresses up to 6.2 GPa, while the MWCNTs lose electrical contact due to alternating compressive stress up to 8.9 GPa and tensile stress up to 2.5 GPa during long-term cycling. Under such very large stresses, the more flexible SWCNTs and their stronger van der Waals forces ensure that SiO x @C still has good contact with SWCNTs.

Size-Dependent Confining Effect of Phosphorus inside Carbon Nanotubes for Highly Stable Lithium-Ion Storage

“…An 8 cm −1 of ΔG represents 1% strain in a single CNT, which is about 11 GPa. 64 As shown in Figure 5d, the evolution curve of the red shift of the G band during the lithiation process agrees well with the discharging profile and shows a maximum strain value of 24 GPa when lithiation ends. Upon delithiation, the upshift of the G-band frequency reflects the shortening of the C−C bond, indicating the relaxation of the strain and the volume change recovering of the inner phosphorus.…”

“…The elongation of the C–C bonds can be reflected by the G-band shift (Δ G ) in the corresponding Raman spectra. An 8 cm –1 of Δ G represents 1% strain in a single CNT, which is about 11 GPa . As shown in Figure d, the evolution curve of the red shift of the G band during the lithiation process agrees well with the discharging profile and shows a maximum strain value of 24 GPa when lithiation ends.…”

Effective Encapsulated Strategy throughout Lithiation/Delithiation: Enabling a Stable Interface and Fast Kinetics of Silicon Anode for High-Performance Lithium-Ion Half/Full Batteries

“…Another strategy is the composite of Si with carbon-based materials such as a carbon nanotube and graphene. 16,17 These composites partially alleviate volume expansion and enhance the conductivity of the Si anode.…”

“…However, the abundant surface area of nanostructured Si brings extensive contact with the electrolyte and continuous consumption of electrolyte from the newly exposed Si surfaces caused by repeated volume expansion, resulting in unstable SEI and increased polarization, which are responsible for capacity attenuation. Another strategy is the composite of Si with carbon-based materials such as a carbon nanotube and graphene. , These composites partially alleviate volume expansion and enhance the conductivity of the Si anode. Nevertheless, the organic nature of carbon-based materials hinders the formation of a stable SEI.…”

Rigid-Flexible Coupling Modification Strategy Realized by Combining MXene with C-Coated Microsilicon for Long-Life Li-Ion Battery

“…For example, Li et al coated a carbon (C) layer on the surface of Si nanoparticles to resist their volume expansion, but the rigid C shell is easily damaged by the stress accumulated from the volume expansion during lithiation. To ensure conductivity while improving the flexibility of the buffer layer, research has focused on developing some flexible conductive substrates, such as graphene − and carbon nanotubes. − However, the preparation process of graphene and carbon nanotubes often requires harsh conditions or involves complex synthesis processes that add extra cost to the product. − Comparatively, MXene, as a novel transition metal carbide or nitride, combines the properties of graphene and graphene oxide with good electrical conductivity, surface chemistry, hydrophilicity, and excellent mechanical properties, which can be used as a good conductive substrate material. − Moreover, its preparation method by etching in LiF-dissolved HCl solution is simple and mild, and it is suitable for large-scale production and application. The general structural formula of MXene is M n +1 X n T x ( n = 1, 2 or 3), in which M represents the former transition metal element, X represents the carbon or/and nitrogen, and T x represents the surface functional group associated with the M layer, such as −F, −O, −OH, etc. , Among them, Ti 3 C 2 T x is the most representative of the MXenes family and has been applied as a conductive buffer substrate for silicon-based anodes.…”